Angle between start and current rotation

Question

I'm facing problem of the operations on rotations. I have a wheel with a start rotation of (0, 0, 0). The player has to rotate wheel 270 degrees in Y axis either left or right.

During the rotation slider should indicate progress of the rotation. For example if player rotated 135 degrees in right direction, slider is 50% filled to the right.

The thing is that I'm not sure how to get the value of which the player rotate the object. For example when I start rotating right my angle changes from (0, 0, 0) to (0, 359, 0). How can I resolve this issue so it knows that change from (0, 0, 0) to (0, 359, 0) means player rotated only +1 degree?

Answer 1

We can keep track of how many quarter-turns we've travelled, counter-clockwise from the start angle (this can go negative for clockwise turns). Then we can measure our current angle relative to the last quarter-turn milestone we crossed.

Because that milestone is never more than 90 degrees away from our angle last frame, we can move just shy of 90 degrees further in a single step and still unambiguously find the total rotation travel.

Then we can update the number of quarter-turns if we've crossed into a new quadrant.

public Transform wheel;   

public float totalAngle;

float _startAngle;
int _quarterTurns = 0;

void Start() {
    _startAngle = wheel.eulerAngles.z;
}

void Update() {
    float currentAngle = wheel.eulerAngles.z;

    // Compute the total angle at the last milestone.
    float milestoneAngle = _startAngle + _quarterTurns * 90;

    // Get the shortest signed difference from the last milestone (-180 to 180)
    float fromMilestone = Mathf.DeltaAngle(milestoneAngle, currentAngle);

    // Our total angle is the sum of the last milestone and our deviation from it.
    totalAngle = milestoneAngle + fromMilestone;

    // If we've crossed another 90-degree increment, update our milestone for next frame.
    if (Mathf.Abs(fromMilestone) >= 90) {
        _quarterTurns += Mathf.RoundToInt(fromMilestone)/90;
    }
}